Microscopes capable of three-dimensional imaging of biological cells and their internal structures are generally based on digital tomographic techniques and are often based on the use of marker dyes to enhance the intensity contrast between components of the cell. Marker dyes however may affect the matter to be observed, particularly in the case of living cells, and also render the procedure more complex. A marker free non-invasive microscopy method based on 3D refractive index computation is described in international patent application PCT/IB2011/051306. The capture of the image data needed to compute a refractive index based image of very small objects with sufficient detail of the internal structure requires however a microscope that is very precise. The precision of conventional microscopes depends on the quality of the lenses and very low manufacturing tolerances in the assembly of the various components of the microscope. This leads to a costly microscope. Moreover, in order to have a high numerical aperture in order to increase the resolution of the captured data, the available working distance and space for the sample to be observed is very limited. This complicates the preparation of the specimen or sample for viewing by the microscope and limits the type of samples that may be observed and the forms in which they may be presented.